Cardiac rhythm management devices are used for providing pacing stimulation to one or more heart chambers in an attempt to improve the rhythm and coordination of atrial and/or ventricular contractions. In cardiac resynchronization therapy (CRT), for example, a number of leads are typically delivered transvenously into or near the heart and include a number of lead electrodes that contact the myocardium for sensing cardiac electrical activity and for delivering electrical stimulation therapy to the heart. Some cardiac pacemakers are capable of delivering CRT therapy by pacing multiple heart chambers. In some techniques, for example, pacing pulses are delivered to multiple heart chambers in a sequence that causes the heart chambers to contract in synchrony, increasing the pumping power and efficiency of the heart. In the case of dysynchrony of the right and left ventricular contractions, for example, biventricular pacing therapy may be used to pace one or both of the ventricles to increase cardiac output. In other techniques, biatrial pacing or pacing of all four heart chambers may be performed to increase cardiac output.
Lead delivery in CRT applications typically involves the delivery of multiple leads to different target pacing sites in or near the heart. In some applications, this process may involve the manipulation of a lead through the coronary sinus and into a branch cardiac vessel located adjacent to the left side of the heart such as a middle branch cardiac vein or posterior branch cardiac vein. Typically, the clinician must manipulate the lead to a target pacing site in or near the heart and, once in place at the site, connect a number of electrical clips to the lead to enable various sensing and impedance measurements to be taken via a pacing system analyzer (PSA) or programming device. In some cases, the implantation of the lead is performed using a venogram by injecting a contrast dye into the patient's blood stream and then determining, for that specific patient, which branch vessel to select using a fluoroscopic monitor.
Lead placement for CRT applications is often accomplished by an iterative trial and error process, in many cases requiring the clinician to manipulate the lead and test the efficacy of the pacing site multiple times before a suitable location is found. The selection of the lead pacing site can have a significant impact on the hemodynamic response to CRT therapy. Consequently, to determine an appropriate pacing site, some CRT implantation techniques involve measuring various timing intervals between each implanted lead electrode and a reference point such as another lead electrode located within the body or a surface EKG electrode. In a biventricular synchronization system in which left ventricular pacing therapy is to be provided, for example, a timing interval between first and second features associated with left ventricular depolarization (e.g., Q-LV or Q1-LV) may be computed for each proposed left ventricular pacing site that results in activation. Based on the timing intervals associated with the patient's responsiveness to CRT, the clinician may then determine the selection of a site based on the location of the latest activation. Other factors such as the size of the vessel and the ease of implanting the lead at the target site may also be considered by the clinician in determining the selection of a site for lead implantation.